1. Field of the Invention
This invention relates to a process for preparing .alpha.-chloro-.epsilon.-caprolactam which is a useful intermediate in the synthesis of L-lysine from .epsilon.-caprolactam. L-lysine is an essential amino acid and is a necessary part of the diet of certain mammals. .alpha.-Chloro-.epsilon.-caprolactam is also a useful monomer in producing chlorine-containing nylon polymers.
2. Brief Description of the Prior Art
.epsilon.-Caprolactam has long been recognized as a potential starting material for making sythetic L-lysine. One synthetic scheme for making L-lysine from .epsilon.-caprolactam involves the chlorination of .epsilon.-caprolactam to form .alpha.-chloro-.epsilon.caprolactam, which is treated with ammonia to form .alpha.-amino-.epsilon.-caprolactam, which then may be subjected to a resolution-racemization technique as described in U.S. Pat. No. 3,941,776 to recover L-.alpha.-amino-.epsilon.-caprolactam, which is in turn hydrolyzed to L-lysine. A major problem with this particular synthetic approach to L-lysine starting with .epsilon.-caprolactam is presented by the first step, i.e. the chlorination of .epsilon.-caprolactam to form .alpha.-chloro-.epsilon.-caprolactam. Direct chlorination of .epsilon.-caprolactam usually leads to the .alpha.,.alpha.-dichloro-.epsilon.-caprolactam, which then must be reduced to form the .alpha.-chloro-.epsilon.-caprolactam. This is an economically unattractive procedure. Various other methods have been described in the literature for the direct chlorination of .epsilon.-caprolactam but they suffer from either chlorination of the nitrogen atom, low yields, require expensive solvents, or are poorly reproducible.
However, the chlorination of N-benzoyl-.epsilon.-caprolactam to N-benzoyl-.alpha.-chloro-.epsilon.-caprolactam in good yield is known in the prior art as exemplified in U.S. Pat. No. 3,096,325 (March 1963).
Exchange reactions involving .epsilon.-caprolactam or its derivatives are not well known and are only briefly described in the prior art. A caprolactam derivative is described as taking part in an exchange reaction involving an organic radical in the synthesis of .epsilon.-caprolactam and 0-acetyl-cyclohexanone oxime from the transfer of an acetyl group from N-acetyl-.epsilon.-caprolactam to cyclohexanoneoxime (Fujita, et al., U.S. Pat. No. 3,767,648). N-acyl-.epsilon.-caprolactams are reported to be efficient acylating agents for amines, [Ramos, et al., Anales real soc. espan. fis. & Chim. (Madrid) 56B, 833 (1956)]. A linear polyamide (Nylon 6) has also been shown to undergo transamidation in a very specialized case with acetamide as reported by the above authors in the same journal volume 52B, 735-8 (1956). However, a transamidation reaction occurring between two different caprolactam molecules is not known in the prior art.
It is an object of this invention to provide a process for preparing .alpha.-chloro-.epsilon.-caprolactam by a transamidation reaction between N-substituted-.alpha.-chloro-.epsilon.-caprolactam and .epsilon.-caprolactam.
It is a further object of this invention to provide a continuous process for preparing .alpha.-chloro-.epsilon.-caprolactam by a transamidation reaction between N-substituted-.alpha.-chloro-.epsilon.-caprolactam and .epsilon.-caprolactam.